1. Field of the Invention
The present invention relates to the technical field of touch panels and, more particularly, to an in-cell multi-touch display panel system.
2. Description of Related Art
The principle of touch panels is based on different sensing manners to detect a voltage, current, acoustic wave, or infrared to thereby detect the coordinate of a touch point on a screen as touched by a finger or other objects. For example, a resistive touch panel uses a voltage difference between the upper and lower electrodes to compute the position of a pressed point for detecting the location of the touch point, and a capacitive touch panel uses a capacitance change generated in an electrostatic combination of the arranged transparent electrodes with the touching part of a human body to generate a current or voltage for detecting the coordinate of the touching part.
Upon the principle, the capacitive touch technologies can be divided into a surface capacitive touch sensing and a projected capacitive touch sensing. The surface capacitive touch sensing has a simple configuration, but the multi-touch implementation is not easy, and the problems of electromagnetic disturbance (EMI) and noises are difficult to be overcome. Therefore, the popular trend of capacitive touch development is toward the projected capacitive touch sensing.
The projected capacitive touch sensing can be divided into a self capacitance and a mutual capacitance sensing. The self capacitance sensing indicates that a capacitance coupling is generated between a touch object and a conduct line, and a touch occurrence is decided by measuring a capacitance change of the conduct line. By contrast, the mutual capacitance sensing indicates that a capacitance coupling is generated between two adjacent conduct lines when a touch occurs.
A typical self capacitance sensing senses the grounded capacitance (Cs) on every conduct line. Thus, a change of the grounded capacitance is used to determine whether an object is approached to the capacitive touch panel. The self capacitance or the grounded capacitance is not a physical capacitor, but parasitic and stray capacitance on every conduct line. FIG. 1 is a schematic view of a typical self capacitance sensing. As shown in FIG. 1, at the first time interval, the driving and sensing units 110 in a first direction drive the conduct lines in the first direction to charge the self capacitance (Cs) of the conduct lines in the first direction. At the second period, the driving and sensing units 110 sense the voltages on the conduct lines in the first direction to obtain m data. At the third period, the driver and sensors 120 in a second direction drive the conduct lines in the second direction to charge the self capacitance of the conduct lines in the second direction. At the fourth period, the driving and sensing units 120 sense the voltages on the conduct lines in the second direction to obtain n data. Therefore, there are m+n data obtained in total.
The typical self capacitance sensing of FIG. 1 connects both a driving circuit and a sensing circuit on the same conduct line in order to drive the conduct line and sense a signal change on the same conduct line to thereby decide a magnitude of the self capacitance. In this case, the advantages include:
(1) reduced amount of data since the typical touch panel has m+n data in a single image only, so as to save the hardware cost;
(2) reduced time required for sensing a touch point since an image raw data can be quickly fetched due to only two sensing operations, i.e., concurrently (or one-by-one) sensing all the conduct lines in the first direction and then in the second direction, for completing a frame, as well as reduced time required for converting a sensed signal from analog into digital; and
(3) lower power consumption due to the reduced amount of data to be processed.
However, such a self capacitance sensing also has the disadvantages as follows:
(1) When there is a floating conductor (such as a water drop, an oil stain, and the like) on the touch panel, it may causes an error decision on a touch point; and
(2) When there are multiple touch points concurrently on the touch panel, it may cause a ghost point effect, resulting in that such a self capacitance sensing cannot be used in multi-touch applications.
In addition, another method of driving the typical capacitive touch panel is to sense a magnitude change of mutual capacitance Cm to thereby determine whether an object is approached to the touch panel. Likewise, the mutual capacitance Cm is not a physical capacitor but a mutual capacitance between the conduct lines in the first direction and in the second direction. FIG. 2 is a schematic diagram of a typical mutual capacitance sensing. As shown in FIG. 2, the drivers 210 are located on the first direction (Y), and the sensors 220 are located on the second direction (X). At the upper half of the first time interval T1, the drivers 210 drive the conduct lines 230 in the first direction and use the voltage Vy_1 to charge the mutual capacitance (Cm) 250, and at the lower half, all sensors 220 sense voltages (Vo_1, Vo_2, . . . , Vo_n) on the conduct lines 240 in the second direction to obtain n data. Accordingly, m*n data can be obtained after m driving periods.
Such a mutual capacitance (Cm) sensing has the advantages as follows:
(1) It is easily determined whether a touch is generated from a human body since a signal generated from a floating conductor is in a different direction than a grounded conductor; and
(2) Every touch point is indicated by a real coordinate, and the real position of each point can be found when multiple points are concurrently touched, so that such a mutual capacitance (CO sensing can easily support the multi-touch applications.
A typical flat touch display is produced by stacking the touch panel directly over the flat display. Since the stacked transparent panel is transparent, the image can be displayed on the touch panel stacked over the flat display, and the touch panel can act as an input medium or interface.
However, such a way requires an increase of the weight of the touch panel due to the stack resulting in relatively increasing the weight of the flat display, which cannot meet with the requirement of compactness in current markets. Furthermore, when the touch panel and flat display are stacked directly, the increased thickness reduces the transmittance of rays and increases the reflectivity and haziness, resulting in greatly reducing the display quality of the screen.
To overcome this, the embedded touch control technology is adapted. The currently developed embedded touch control technologies are essentially on-cell and in-cell technologies. The on-cell technology uses a projected capacitive touch technology to form a sensor on the backside (i.e., a surface for attaching a polarized plate) of a color filter (CF) for being integrated into a color filter structure. The in-cell technology embeds sensors in an LCD cell to thereby integrate a touch element with a display panel such that the display panel itself is provided with a touch function without having to be attached or assembled to a touch panel. Such a technology typically is developed by a TFT LCD panel factory. The in-cell multi-touch panel technology is getting more and more mature, and since the touch function is directly integrated during a panel production process, without adding a layer of touch glass, the original thickness is maintained and the cost is reduced.
FIG. 3(A) is a schematic view of a configuration of a typical in-cell multi-touch panel 300. In FIG. 3(A), the panel 300 includes a lower polarizer 310, a lower glass substrate 320, a thin film transistor (TFT) or LTPS layer 330, a liquid crystal (LC) layer 340, a common voltage and touch driving layer 350, a color filter layer 360, an upper glass substrate 370, a conductive electrode layer 380, and an upper polarizer 390. As shown in FIG. 3(A), in order to save the cost, a touch sensor is integrated with an LCD panel, and the common voltage layer of the LCD panel is located at a layer as same as the drivers of the touch sensor, thereby forming the common voltage and touch driving layer 350, so as to achieve the cost saving. The conductive electrode layer 380 is located on the upper glass substrate 370. The TFT or LTPS layer 330 is constructed of thin film transistors (TFTs) or low-temperature poly-Si film transistors (LTPS) 332 and transparent electrodes 331.
FIG. 3(B) is a schematic view of another configuration of a typical in-cell multi-touch panel. As compared with FIG. 3(A), the difference in FIG. 3(B) is that the conductive electrode layer 380 is located beneath the upper glass substrate 370.
FIG. 3(C) is a schematic view of yet another configuration of a typical in-cell multi-touch panel. As compared with FIG. 3(A), the difference in FIG. 3(C) is that the common voltage and touch driving layer 350 is located beneath the LC layer 340.
FIG. 3(D) is a schematic view of a further configuration of a typical in-cell multi-touch panel. As compared with FIG. 3(C), the difference in FIG. 3(D) is that the conductive electrode layer 380 is located beneath the upper glass substrate 370.
The configuration of the in-cell multi-touch panel in any one of FIGS. 3(A), 3(B), 3(C) and 3(D) uses a time sharing to divide the time for one display frame into a display cycle and a touch cycle to thereby commonly use the common voltage layer of the display panel and the driving layer of the touch sensor. The timings for FIGS. 3(A), 3(B), 3(C) and 3(D) are shown in FIGS. 4(A), 4(B), 4(C) and 4(D), respectively.
As shown in FIG. 4(A), the time for one display frame is divided into one display cycle and one touch cycle, and the frame of the display panel is displayed in the display cycle before the touch sensing is performed in the touch cycle. As shown in FIG. 4(B), the touch sensing is performed before the frame of the display panel is displayed. As shown in FIG. 4(C), partial lines of one frame are displayed in a section A; then the touch sensing is performed; finally the remaining lines of the frame are displayed in a section B. As shown in FIG. 4(D), a display of the vertical synchronous signal (Vsync) is changed such that the frame of the display panel is displayed when the vertical synchronous signal (Vsync) is at a high level. Conversely, when the vertical synchronous signal (Vsync) is at a low level, the touch sensing is performed.
In US Patent Publication 2012/0050217 entitled “Display device with touch detection function, control circuit, driving method of display device with touch detection function, and electronic unit”, the timing of the first embodiment (shown in FIG. 8 of the patent publication) is as same as that in FIG. 4(A), in which the frame is displayed before the touch sensing is performed. The timing of the second embodiment (shown in FIG. 17 of the patent publication) is as same as that in FIG. 4(C), in which the partial lines of the frame is displayed in the section A; then the touch sensing is performed; finally the remaining lines of the frame is displayed in the section B. The timing of the third embodiment (shown in FIG. 19 of the patent publication) is similar to the first embodiment, i.e., as same mode as in FIG. 4(A) except that a toggle of the common voltage layer is used as a trigger for the touch sensing. The first and third embodiments use the time sharing to perform the touch sensing on every line to be displayed, and the second embodiment uses the time sharing to perform the touch sensing on every frame to be displayed. However, either the first embodiment, the third embodiment, or the second embodiment may sacrifice the settling time for the display data and the touch data.
For such a time sharing, as the resolution of the display panel is getting higher, the number of pixels to be driven by the display driver IC is getting more, and thus the time required becomes longer In this case, the display frame rate has to be maintained at 60 Hz or above, i.e., each frame only contains 16.6 ms. However, it is increasingly difficult to perform the image displaying and touch sensing in 16.6 ms due to the higher and higher resolution of the display panel. Therefore, the increasing image resolution is limited.
Accordingly, it is desirable to provide an improved in-cell multi-touch display panel system to mitigate and/or obviate the aforementioned problems.